Tidal Wetlands

Tidal wetlands are an important geomorphic and ecological feature of the coastal zone. Our projects deal with the physical forcings that affect wetland stability over event-to-annual timescales, including wave attack, sediment supply, and sea-level rise.

Tidal wetland complexes are geomorphic features composed of vegetated marsh plain, intertidal flats, and tidal channels. The stability of a tidal wetland complex is a function of interconnected biogeomorphic and physical processes. We are primarily studying the influence of sediment supply through tidal channels, wave attack on marsh faces, and feedbacks between vegetation and hydrodynamics.

Tidal channels deliver sediment to the vegetated subaerial marsh plain on high tides, which tends to increase the elevation of the marsh plain through time. Prior work suggests that marsh plains and channel networks develop simultaneously, moving toward an equilibrium condition where the net sediment flux through the channel network channels equals zero, and the transfer of sediment from channel to marsh platform balances sea level rise. Therefore, measurements of the concentration and flux of sediments through tidal channels represent a spatially integrated measure of marsh stability.

conceptual model of wetlands

Conceptual model of sediment transport to tidal wetlands from four locations (Ganju et al., 2013). ETM indicates estuarine turbidity maximum.

Recent work has highlighted the ephemeral nature of salt marshes, pointing out the balance between erosive forces and sediment supply. Wave attack on marsh faces is a primary erosive force, and causes marsh banks to slump, thereby liberating sediment from the marsh plain. Under low external sediment supply conditions, this leads to an overall landward migration of the marsh plain. We are exploring the connections between wave attack, marsh erosion, sediment supply, and ecosystem services through site-specific studies and larger scale syntheses of existing data.

Publications:

Ganju, N.K., Defne, Z., Kirwan, M.L., D’Alpaos, A., Carniello, L., and Fagherazzi, S., 2017. Spatially integrative metrics reveal hidden vulnerability of microtidal salt marshes. Nature Communications, 8, 14156. (ganju_et_al_vulnerability.pdf)

Leonardi, N., Defne, Z., Ganju, N.K. and Fagherazzi, S., 2016. Salt marsh erosion rates and boundary features in a shallow Bay. Journal of Geophysical Research: Earth Surface. (leonardi_et_al_erosion.pdf)

Ganju, N.K., Kirwan, M.L, Dickhudt, P.J., Guntenspergen, G.R., Cahoon, D.R., and Kroeger, K.D., 2015, Sediment transport based metrics of wetland stability, Geophysical Research Letters. (ganju_et_al_metrics.pdf)

Leonardi, N., Ganju, N.K., and Fagherazzi, S., 2015, Absence of a critical threshold for erosion determines salt-marsh survival during violent storms and hurricanes, Proceedings of the National Academy of Sciences. (leonardi_et_al_PNAS.pdf)

Rosencranz, J.A., Ganju, N.K., Ambrose, R.F., Brosnahan, S.M., Dickhudt, P.J., Guntenspergen, G.R., MacDonald, G.M., Takekawa, J.Y, and Thorne, K.M., 2015, Balanced sediment fluxes in southern California’s Mediterranean-climate zone salt marshes, Estuaries and Coasts, DOI 10.1007/s12237-015-0056-y. (rosencranz_et_al_fluxes.pdf)

Ganju, N.K., Nidzieko, N.J., and Kirwan, M.L., 2013, Inferring tidal wetland stability from channel sediment fluxes: observations and a conceptual model, Journal of Geophysical Research-Earth Surface, 118, 114. (ganju_et_al_stability.pdf).

Ganju, N.K., Schoellhamer, D.H., and Bergamaschi, B.A, 2005, Suspended sediment fluxes in a tidal wetland: measurement, controlling factors, and error analysis. Estuaries 28(6), 812-822. (ganju_et_al_BI.pdf)

 

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